Electrochemical sensors comprising a selfsupporting ion-sensitive polymeric membrane are well known in the art. In use, such membranes separate a solution being tested from an internal reference solution. Such sensors have membranes that are self-supporting, which need not be coated on a solid-state electrode body. For example, U.K. Pat. No. 2,076,545 describes such a sensor in which the membrane comprises a copolymer having ion-exchange sites with the copolymer having a glass transition temperature (T.sub.g) less than 20.degree. C. Such a copolymer is very difficult to prepare, often resulting in a non-functioning sensor.
Electrochemical sensors comprising a solid-state electrode body having an ion-sensitive polymeric membrane coated on a surface thereof are also well known. For example, U.S. Pat. No. 4,020,830 describes a chemical sensitive field effect transistor transducer capable of selectively detecting and measuring chemical properties of substances to which the transducer is exposed. The transducer includes a semiconductor substrate material having a certain doping polarity, a pair of spaced apart diffusion regions located at the surface of the substrate material and having a doping polarity opposite to that of the substrate material, electrical insulating material overlying the diffusion regions and the surface of the substrate material lying between the diffusion regions, and a chemical selective system overlying the insulator material. The chemical selective system may be an ion-sensitive polymeric membrane such as a membrane comprising a polyvinyl chloride matrix having an ion-exchange material dispersed therein.
It is also known to use such an ion-sensitive polymeric membrane in an electrochemical sensor of the coated wire electrode type where the membrane is coated on the surface of a solid electron conductor, such as a metal wire. The membrane in such sensors allows a selective ion exchange to occur between the ion-exchange material and a solution to which the membrane is exposed. The potential difference generated electrochemically between the membrane and the solution may be used to measure the concentration of a particular ion in solution.